This invention pertains to an ocular fundus camera system and methodology. Hereinafter in the discussion of this field, and in the description presented regarding the present invention, the single term “fundus” will be used in most instances, with the understanding that all such references relate to the ocular fundus.
The inside back surface of the eye, which contains the retina, the blood vessels, and the neural tissue, is called the ocular fundus. Many systemic pathologies, as well as ocular ones, cause changes in the appearance of the fundus, and as a consequence, virtually all ophthalmic exams, and most general physical exams, include observations of the fundus. Such observations are most often performed using a device called an ophthalmoscope, a hand-held device that provides the observer with a magnified direct view of the fundus through a subject's pupil.
Unfortunately, there are many factors that limit the usefulness of ophthalmoscope examinations. Among the major ones of these limitations are (a) that most ophthalmoscopes have rather poor optical resolution—a factor considerably limiting the fundus detail which is visible, (b) that continuous eye movement makes observation very challenging, (c) that the opportunity for clarity-enhancing image magnification is minimal, and (d), that, in the use of an ophthalmoscopic device, no permanent record of an examination is created.
To overcome these difficulties, in a mode aimed essentially at functional replacement of the use of ophthalmoscopic devices, certain prior art camera systems and associated methodologies have been developed which operate in various ways to capture, hopefully in the best way possible, detailed images of the fundus—thus to enable more precise and confident examination of the various conditions which may be detected through observing a clear image of the fundus.
The present invention focuses attention generally in this same area of ocular-fundus camera systemic and methodologic development, but does so in a manner which turns out to offer an improved and very high degree of extremely well-focused image accuracy, and in a system and methodologic approach which is relatively simple, and which can be systemically constructed, and methodologically used with camera equipment, and related optical and electronic (including digital computer) components, which are, for various reasons, considerably less costly, and ultimately more accurate in terms of fundus-image clarity, than what have been employed in prior-art.
The invention especially offers, in this setting, significant improvements in the visual (and other) presentation quality of fundus-based information usable in assessing the various kinds of matters regarding which accurate detection of fundus condition is so important. Further, the invention additionally offers a distinctly new way to perform accurate autorefraction.
As will be seen, an important feature of the invention which is highly relevant to both its structural and its operational advantages, is the included presence, systemically, of what is referred to as a light-shifting structure, or optical, light-content shifting structure—a structure which, among other things, (a) greatly simplifies and reduces equipment costs, (b) enhances focusing clarity and accuracy of an obtained fundus image, (c) readily enables the obtaining and presentation of stereo fundus images, and (d) is central to the just-above-mentioned autorefraction capability of the invention.
Accordingly, from one structural point of view, the invention proposes an ocular fundus camera system usable in relation to a light-illuminated fundus in a subject's eye, and including an elongate, main optical path which, in an operative condition of the system, extends downstream from the eye and carries fundus-reflection light derived from, and possessing a reflection image of, the fundus, this system including (a) an image-detecting sensor disposed along the main path at a location which is downstream from the eye in optical communication with fundus-reflection light carried in this path, and (b) structure operatively associated with the sensor, upstream from the eye, for introducing, into light reflected from the fundus, edge-portion-containing optical contrast imagery having at least one, contrast edge portion whose spatial disposition in the fundus-reflection light is independent of eye movement.
From another structural perspective, the invention features an ocular fundus camera system which, in an operative condition, includes (a) light-source structure for illuminating, along an elongate, illumination path, the fundus in a subject's eye, (b) an elongate, main optical path having upstream and downstream ends and a long axis, extending downstream from the subject's eye, and carrying, downstream along its length, both light that acts as if the pupil were its source, and light reflected from, and carrying an image of, the fundus (referred to also herein as fundus reflection light), (c) an image-detecting sensor centered on the main path's long axis adjacent the latter's downstream end, disposed for optical communication with light carried in the main path, (d) an aperture also centered on the main path's long axis, operatively associated with, and stationary with respect to, the sensor at a location which is upstream along the main path from the sensor, positioned there to communicate to the sensor light carried in the main path, (e) discriminatory, light-content shifting structure disposed centrally on the main path's long axis upstream therealong relative to the aperture, operable selectively for producing, within that portion of the main path which is disposed intermediate the shifting structure and the aperture, relative trans-axial displacement-shifting solely of any non-collimated light carried in that portion of the main path which is disposed immediately upstream from the shifting structure, and (f) structure selectively placeable across the illumination path for introducing, effectively, into light reflected from the fundus, edge-containing optical contrast imagery having at least one, contrast edge portion which lies at an angle relative to the direction of trans-axial shifting producible by the shifting structure, and whose spatial disposition in the fundus-reflection light is independent of eye movement.
From still a further structural point of view, what the present invention proposes is an ocular fundus camera system usable in relation to a light-illuminated fundus in a subject's eye, including, as cooperative, systemic elements, (a) an image-detecting sensor (preferably electronic) disposed centrally along, and adjacent the downstream end of, a main optical path which extends downstream from a subject's eye for receiving an image reflected from the illuminated fundus, (b) a fundus-image-passing (to the sensor) aperture centered on the main path's long axis at a location which is upstream from, and, significantly, stationary relative to, the sensor, and (c) disposed appropriately upstream from the aperture, discriminatory, light-content shifting structure, operable selectively for producing, within that portion of the main optical path which extends immediately downstream from the shifting structure, relative trans-axial displacement solely of any non-collimated light carried in that portion of the main optical path which is disposed just upstream from the shifting structure.
The concept of discriminatory, relative trans-axial light-flow (light-content) displacement refers to the ability of the light-shifting structure to discriminate, “in a shifting sense”, between collimated and non-collimated light.
The system of the invention, in still a more specific manner of thinking about it additionally includes an appropriately (conventionally) algorithmically programmed digital computer which is operatively connected to selected system elements, including the sensor from which it is adapted to receive sensor-detected imagery. By inclusion of this thus-involved computer, any relative trans-axial displacement produced by the light-shifting structure, which displacement is then detected by the sensor, and through the sensor also by the connected computer, causes the computer to respond to detected light-shifting in a manner designed, under precision computer control, to minimize, via certain systemic optical adjustments, the presence of non-collimated fundus reflection light carried in that portion of the main optical path which is disposed upstream from the shifting structure. Such minimizing activity functions accurately to achieve dramatically clear focus of a fundus image on the sensor. The amount and direction of detected light shifting furnishes the necessary, relevant, fundus-image focus-correcting information to the computer.
In the preferred and best-mode embodiment of, and manner of practicing, the invention, the light-shifting structure takes the form of what we call a parallel plane shifter—a flat (i.e., having a plane), parallel-flat-opposite-sided piece of optically clear glass, herein having a chosen thickness of about 12.5-mm, and a circular, perimetral outline with a diameter of about 1-inches. Other sizes and shapes may be chosen for use, if desired depending upon other, freely user chooseable, system design features. This parallel plane shifter is also referred to herein as a discriminatory, light-content shifting structure, as an optical, light-content shifting structure, and as a device which is operable to produce a certain character of relative, trans-axial, light-flow displacement which will be explained later herein.
There are other interesting, and to some extent tangential, structural aspects of, and structural, collateral considerations associated with, the system of the invention as just generally discussed above, such as a few which involve, essentially, optical-element positioning and tracking, both manual (where appropriate), and under computer control, relative to the eye. Many of these other matters concern conventional practices that are not central to the system-internal optical features which are newly offered by the invention, and accordingly, while mentioned at appropriate points in the detailed description of the invention, are not specifically elements of the invention. These other matters, therefore, beyond the making of simple references to them, and recognized to be implementable in a variety of different ways, are left, for systemic implementation, appropriately “in the hands” of those generally skilled in the relevant art who are very knowledgeable about them.
From one operational point of view, the invention proposes an ocular fundus-imaging camera methodology usable, in relation to a light-illuminated fundus in a subject's eye, to apply to an image sensor a precision-focused image of the fundus contained in an elongate flow of reflection light coming from the fundus, this methodology including the steps of (a) discriminatorily, effecting trans-axial light-flow shifting, in a defined portion of the reflection flow, and relative to the long axis of that flow, solely of non-collimated light present in that defined portion, and (b) achieving fundus image focus by performing an operation which prevents any such shifting with respect to the reflection-carried fundus image content, per se.
From another operational perspective, the invention sets forth an image-forming, ocular fundus camera methodology including (a) placing, by external illumination, and projection onto the fundus, a contrast image possessing a contrast edge whose spatial position is independent of eye movement, (b) by such placing, creating, in a main, external optical path, a reflection-flow from the fundus which contains an image of the contrast edge which, depending upon the existence or absence of correct fundus focus, will be contained, respectively, in either collimated or non-collimated light, and (c) achieving proper fundus focus by making an adjustment to assure that, within the main optical path, the contrast-edge image content carried therein is present in collimated light.
From still a further operational viewpoint, and in relation to the invention's autorefraction capability, the present invention presents an ocular fundus camera methodology including the steps of (a) illuminating the fundus in a subject's eye along a main optical path having a long axis, (b) by such illuminating, creating a light reflection from the fundus which flows therefrom outwardly through the pupil in a flow of reflection light which is directed downstream from the eye along the main optical path's long axis, (c) discriminatorily, and in a relative trans-axial displacement manner at a location along the main optical path which is disposed downstream from the eye, shifting solely any non-collimated light which is contained in the flow of created reflection light, (d) detecting any such shifting, and (e) employing any detected shifting in a manner designed to aid in performing autorefraction.
Practice of the invention additionally features an ocular fundus, image-focusing—camera methodology expressible as including (a) illuminating the fundus in a subject's eye along an elongate illumination path, (b) by such illuminating, creating a light reflection from the fundus directed therefrom outwardly through the pupil in a flow of reflection light which progresses downstream from the eye along an elongate main optical path having a long axis, (c) discriminatorily, and in a relative trans-axial displacement manner at a location along the main optical path which is disposed downstream from the eye, shifting solely any non-collimated light which is contained in the flow of created reflection light, (d) detecting any such shifting, and (e) employing any detected shifting in a manner designed to minimize the presence of non-collimated light in the reflection-light flow.
Commenting on the invention methodology with a bit more specificity, the mentioned shifting is preferably performed by selected rotation, on the long axis of the mentioned main optical path, of a rotatable parallel plane shifter there placed in a condition with its plane disposed at a modest (such as about 9-degrees) angle relative to a plane disposed normal to the main optical path's long axis.
Even more specifically, the invention methodology further includes, in a manner non-movably centered on the main optical path's long axis, and at another location along that axis (than where the mentioned parallel plane shifter is disposed), which other location is located downstream from the shifter location, aperturing a portion of the flow of reflection light, and, downstream from where aperturing takes place, and at the location wherein the mentioned detecting occurs, performing such detecting by electronically sensing the apertured light-flow portion, with the step featuring minimization of non-collimated light presence in the reflection light flow involving using an outcome (by way of computer action) of the performing of electronic sensing. The verbal term “aperturing” is introduced and employed herein to mean the act of directing a light flow through a defined optical aperture, as in a camera.
Non-movability, relative to the main optical path's long axis, of that which performs aperturing, according to the invention, combined with the discriminatory light-shifting behavior, and use, of a parallel plane shifter, are significant invention features—fundus-imaging advances—which allow, among other things, for the use of inexpensive, electronic (digital) camera equipment for optical image sensing and image presentation.
As explained generally above, the minimizing of non-collimated light presence in the reflection light flow effects focusing of the apertured light flow at the location where sensing occurs so as to obtain a well-focused image of the illuminated fundus.
Other methodologic features of the invention, of course, exist, and these other such features, along with the above-mentioned, and other, systemic structural features of the invention, will become more fully apparent as the detailed description of the invention presented below is read in conjunction with the accompanying drawings.